It is easy to multiply goji berries.
Take some cuttings in spring. Dip them into a jar of water. If it is not freezing, just put them outside or put them next to a window. Change the water every day or two. Once they start sending out roots, you can transplant them to a pot or to the ground.
If you live in Florida with summer rain, you can cut and root them in soil in any season. Both berries and leaves are edible.
Cut a branch, eat the leaves, then multiply. Or you can eat the fruits, collect the seeds, and plant the seeds. Either way is very easy.